Air operated double diaphragm pumps include air driven diaphragms positioned on each side of the center section of the pump and are commonly used in industry to pump a variety of substances, including paint, peanut butter, sludge, abrasive chemicals, etc.
Pressurized air from an air compressor or other source of pressurized air enters the pump through an actuator valve and passes into the center section of the pump. The air will then be directed to an air chamber on the air side of one of the diaphragms, depending on the position of the reciprocable valve spool within the actuator valve. The valve spool reciprocates constantly during operation of the pump to alternately direct air against the air sides of opposed diaphragms.
The two diaphragms are mechanically connected by a control rod passing through the center section of the pump. As one diaphragm outwardly expands under pressure of the air and expels slurry from the slurry side of that diaphragm, the control rod pulls the other diaphragm inwardly to draw slurry into the slurry side of said other diaphragm. The process is repeated as long as the valve spool reciprocates within the actuator valve.
The valve spool sometimes stalls, and the pump stops, because of foreign matter in the air supply or fluctuation of the air pressure. When pressurized air remains in the pump, the usual remedy for a stalled actuator valve is to bang on the actuator valve in an effort to free the valve spool. This is sometimes successful but it is hard on the pump.
U.S. Pat. No. 4,339,985 issued July 20, 1982 to Wilden for AIR DRIVEN RECIPROCATING DEVICE shows one device for reducing the risk of the valve spool stalling, but it is not entirely successful.